Update the documentation

_examples/q/q.go

@@ -94,9 +94,7 @@ Flags:
 		opt.SetDo()
 		opt.SetUDPSize(dns.DefaultMsgSize)
 		if *nsid {
-                        opt.Option = make([]dns.Option, 1)
-                        opt.Option[0].Code = dns.OptionCodeNSID
-                        opt.Option[0].Data = ""
+			opt.SetNsid("")
 		}
 		m.Extra = make([]dns.RR, 1)
 		m.Extra[0] = opt

dns.go

@@ -113,7 +113,7 @@ func (h *RR_Header) String() string {
 	return s
 }
 
-// Return the number of labels in a domain name
+// Return the number of labels in a domain name.
 func LabelCount(a string) (c uint8) {
         // walk the string and count the dots
         // except when it is escaped

edns.go

@@ -31,6 +31,14 @@ type Option struct {
  * 	Rdlength      uint16 // length of data after the header
  */
 
+// Adding an EDNS0 record to a message is done as follows:
+//      opt := new(RR_OPT)
+//      opt.Hdr = dns.RR_Header{Name: "", Rrtype: TypeOPT}
+//      opt.SetVersion(0)       // set version to zero
+//      opt.SetDo()             // set the DO bit
+//      opt.SetUDPSize(4096)    // set the message size
+//      m.Extra = make([]RR, 1)
+//      m.Extra[0] = opt        // add OPT RR to the message
 type RR_OPT struct {
 	Hdr    RR_Header
 	Option []Option "OPT" // tag is used in Pack and Unpack
@@ -101,7 +109,7 @@ func (rr *RR_OPT) Do() bool {
         return byte(rr.Hdr.Ttl >> 8) &_DO == _DO
 }
 
-// Set the do bit
+// Set the DO bit
 func (rr *RR_OPT) SetDo() {
         b1 := byte(rr.Hdr.Ttl >> 24)
         b2 := byte(rr.Hdr.Ttl >> 16)
@@ -118,6 +126,7 @@ func (rr *RR_OPT) Nsid() string {
 
 // Set the NSID from a string which is represented as hex characters.
 func (rr *RR_OPT) SetNsid(hexnsid string) {
+        rr.Option = make([]Option, 1)           // TODO(mg) check length first?
         rr.Option[0].Code = OptionCodeNSID
         rr.Option[0].Data = hexnsid
 }

types.go

@@ -341,7 +341,7 @@ func (rr *RR_NAPTR) String() string {
 		rr.Replacement
 }
 
-// RFC 4398
+// See RFC 4398.
 type RR_CERT struct {
 	Hdr         RR_Header
 	Type        uint16